Resistive element

ABSTRACT

A resistive element includes: a resistive layer having a rectangular shape defined by a resistance length direction and a resistance width direction orthogonal to the resistance length direction; a first outer contact and a first inner contact allocated on one side of the resistive layer defined in the resistive length direction; and a second outer contact and a second inner contact allocated on another side of the resistive layer defined in the resistive length direction, wherein, as viewed in the resistance length direction, the first inner contact is shifted from the second inner contact, the first inner contact is at least partly opposed to the second outer contact, and the second inner contact is at least partly opposed to the first outer contact.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims benefit of priority under 35 USC 119 based on Japanese Patent Application No. 2017-238886 filed on Dec. 13, 2017, the entire contents of which are incorporated by reference herein.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a resistive element, more particularly, to a contact arrangement method for a resistive element.

2. Description of the Related Art

JP2003-249565 discloses a resistive element in which metal wires are connected to a thin-film resistive layer. The resistive element disclosed in JP2003-249565 is provided with contact holes open in an insulating film deposited on the resistive layer to connect the resistive layer and the metal wires, and a metal material is buried in the contact holes to obtain conductivity. The contact holes are restricted to having a fixed size, for example, by design rules. Under such restriction, multiple contacts are typically provided in order to reduce an influence of variation of contact resistive components.

The contacts of the resistive element disclosed in JP2003-249565 are arranged at both ends of the resistive layer such that outer contacts are hidden behind inner contacts. A resistivity of the resistive layer is determined by a distance between the inner contacts opposed and closest to each other. While current is concentrated in the inner contacts among the multiple contacts, current components are reduced in the outer contacts, resulting in unevenness of the current components in the respective contacts. Such unevenness of the current components leads to inequality in performance of products or a reduction in resistance to surge current.

SUMMARY OF THE INVENTION

In view of the foregoing problems, the present invention provides a resistive element having larger effective contact areas and eliminating unevenness of current components of contacts.

An aspect of the present invention inheres in a resistive element encompassing: a resistive layer having a rectangular shape defined by a resistance length direction and a resistance width direction orthogonal to the resistance length direction; a first outer contact allocated on one side of the resistive layer defined in the resistive length direction; a first inner contact allocated on the one side of the resistive layer closer to a middle of the resistive layer than the first outer contact in the resistance length direction; a second outer contact allocated on another side of the resistive layer defined in the resistive length direction; and a second inner contact allocated on the other side of the resistive layer closer to the middle of the resistive layer than the second outer contact in the resistance length direction, wherein, as viewed in the resistance length direction, the first inner contact is shifted from the second inner contact, the first inner contact is at least partly opposed to the second outer contact, and the second inner contact is at least partly opposed to the first outer contact.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating a resistive element according to an embodiment of the present invention;

FIG. 2 is a graph showing a relation between a temperature coefficient and a dose amount in doped polysilicon;

FIG. 3 is a plan view illustrating the resistive element according to the embodiment of the present invention;

FIG. 4 is a cross-sectional view additionally illustrating an equivalent circuit superposed on the resistive element according to the embodiment of the present invention;

FIG. 5A and FIG. 5B are circuit diagrams illustrating equivalent circuits of the resistive element according to the embodiment of the present invention;

FIG. 6 is a plan view illustrating a contact arrangement in the resistive element according to the embodiment of the present invention;

FIG. 7 is a plan view illustrating a contact arrangement in a resistive element of a comparative example;

FIG. 8 is a plan view illustrating another contact arrangement in the resistive element according to the embodiment of the present invention;

FIG. 9 is a circuit diagram illustrating the practical application of the resistive element according to the embodiment of the present invention;

FIG. 10 is a cross-sectional view illustrating a process of manufacturing the resistive element according to the embodiment of the present invention;

FIG. 11 is a cross-sectional view continued from FIG. 10 illustrating the process of manufacturing the resistive element according to the embodiment of the present invention;

FIG. 12 is a cross-sectional view continued from FIG. 11 illustrating the process of manufacturing the resistive element according to the embodiment of the present invention;

FIG. 13 is a cross-sectional view continued from FIG. 12 illustrating the process of manufacturing the resistive element according to the embodiment of the present invention;

FIG. 14 is a cross-sectional view continued from FIG. 13 illustrating the process of manufacturing the resistive element according to the embodiment of the present invention;

FIG. 15 is a cross-sectional view continued from FIG. 14 illustrating the process of manufacturing the resistive element according to the embodiment of the present invention;

FIG. 16 is a cross-sectional view continued from FIG. 15 illustrating the process of manufacturing the resistive element according to the embodiment of the present invention;

FIG. 17 is a cross-sectional view continued from FIG. 16 illustrating the process of manufacturing the resistive element according to the embodiment of the present invention;

FIG. 18 is a cross-sectional view continued from FIG. 17 illustrating the process of manufacturing the resistive element according to the embodiment of the present invention;

FIG. 19 is a cross-sectional view continued from FIG. 18 illustrating the process of manufacturing the resistive element according to the embodiment of the present invention;

FIG. 20 is a cross-sectional view illustrating a resistive element according to a first modified example of the embodiment of the present invention; and

FIG. 21 is a cross-sectional view illustrating a resistive element according to a second modified example of the embodiment of the present invention.

DETAILED DESCRIPTION

With reference to the Drawings, an embodiment of the present invention will be described below. In the Specification and the Drawings, the same or similar elements are indicated by the same or similar reference numerals. The drawings are schematic, and it should be noted that the relationship between thickness and planer dimensions, the thickness proportion of each layer, and the like are different from real ones. Accordingly, specific thicknesses or dimensions should be determined with reference to the following description. Moreover, in some drawings, portions are illustrated with different dimensional relationships and proportions. The embodiment described below merely illustrate schematically devices and methods for specifying and giving shapes to the technical idea of the present invention, and the span of the technical idea is not limited to materials, shapes, structures, and relative positions of elements described herein. In addition, in the following description, the definition of the directions such as up and down is merely provided for the convenience of description and does not limit the technical idea of the invention. For example, when an object is rotated by 90 degrees and observed, the direction will be read by changing the up and down to the left and right; and when an object is rotated by 180 degrees and observed, the direction will be read by inverting the up and down.

A resistive element according to an embodiment of the present invention includes a semiconductor substrate 1 having a low specific resistivity, first insulating films 2 a and 2 b deposited on the semiconductor substrate 1, and thin-film resistive layers 3 a and 3 b deposited on the first insulating films 2 a and 2 b, as illustrated in FIG. 1. The resistive element is used as a gate resistor for an insulated-gate bipolar transistor (IGBT), for example.

A thickness of the semiconductor substrate 1 is about 350 micrometers, for example. The semiconductor substrate 1 may be a silicon substrate having a low specific resistivity and doped with a high concentration of n-type impurity ions. A resistive component of the semiconductor substrate 1 is preferably reduced to a level which can be ignored with respect to a resistive component of the resistive layers 3 a and 3 b. In particular, the resistive component of the semiconductor substrate 1 is preferably about one hundredth or less of the resistive component of the resistive layers 3 a and 3 b. The specific resistivity of the semiconductor substrate 1 may be in a range from 2 mΩ·cm to 60 mΩ·cm. Alternatively, the semiconductor substrate 1 may be a silicon substrate doped with a high concentration of p-type impurity ions, or may be made of elements other than silicon.

The first insulating films 2 a and 2 b may be a silicon oxide (SiO₂) film, a silicon nitride (Si₃N₄) film, or a composite film of these films. Alternatively, the first insulating films 2 a and 2 b may be made of an organic silicon compound deposited by a chemical vapor deposition (CVD) method using tetraethoxysilane (TEOS) gas to obtain a TEOS film. A thickness of the first insulating films 2 a and 2 b is about 800 nanometers, for example. An increase in thickness of the first insulating films 2 a and 2 b reduces a parasitic capacitance.

A thickness of the resistive layers 3 a and 3 b is about 500 nanometers, and a sheet resistance of the resistive layers 3 a and 3 b is about 150 Ω/sq, for example. A resistivity of the resistive layers 3 a and 3 b can be controlled by adjusting a width (in a depth direction in FIG. 1) and a length (in a right-left direction in FIG. 1) of the resistive layers 3 a and 3 b. The resistive layers 3 a and 3 b may be made of n-type doped polysilicon. The n-type doped polysilicon can be obtained such that n-type impurity ions such as phosphorus (P) are implanted in polycrystalline silicon (polysilicon), or polycrystalline silicon is added to a stacked layer with a CVD device.

A temperature coefficient of the resistive layers 3 a and 3 b is preferably zero ppm/° C. or lower. In other words, the resistive layers 3 a and 3 b preferably has a temperature coefficient of zero or a negative number. Such a temperature coefficient suppresses an increase in the resistivity during operation at a high temperature. For example, when the resistive element according to the embodiment of the present invention is used as a gate resistor for IGBT, a loss can be reduced when IGBT is turned on. The temperature coefficient of the doped polysilicon can be controlled by adjusting a dose amount of the impurity ions implanted in the polysilicon. FIG. 2 is a graph showing a relation between the temperature coefficient of the n-type doped polysilicon formed by ion implantation of phosphorus (P) and the dose amount of the impurity ions. For example, when the dose amount is set to about 7.0×10¹⁵ cm⁻² or less, the temperature coefficient of the doped polysilicon can be reduced to zero ppm/° C. or lower. The temperature coefficient of the resistive layers 3 a and 3 b is not intended to be limited to zero ppm/° C. or lower. The resistive layers 3 a and 3 b may have a temperature coefficient of a positive number.

The resistive layers 3 a and 3 b may be made of p-type doped polysilicon. The p-type doped polysilicon can be obtained such that p-type impurity ions such as boron (B) are implanted in polysilicon. The resistive layers 3 a and 3 b are not limited to the doped polysilicon, and may be a nitride film of transition metal such as tantalum nitride (TaN_(x)), or a stacked metallic film having a high melting point including a chromium (Cr) film, a nickel (Ni) film, and a manganese (Mn) film stacked in this order. Alternatively, the resistive layers 3 a and 3 b may be a silver-palladium (AgPd) thin film or a ruthenium oxide (RuO₂) thin film. Instead of the structure illustrated in FIG. 1, the resistive layers 3 a and 3 b may be made of a p-type diffusion layer or an n-type diffusion layer deposited on the semiconductor surface.

A second insulating film (interlayer insulating film) 4 is provided to cover the first insulating films 2 a and 2 b and the resistive layers 3 a and 3 b. A thickness of the second insulating film 4 is about 1500 nanometers, for example. The second insulating film 4 may be a non-doped silicate glass (NSG) film, such as a silicon oxide film without containing phosphorus (P) or boron (B) (a SiO₂ film), a phosphosilicate glass (PSG) film, a borosilicate glass (BSG) film, a borophosphosilicate glass (BPSG) film, a silicon nitride (Si₃N₄) film, or a composite of some of these films. For example, the second insulating film 4 may be a composite film including a NSG film of about 770 nanometers and a PSG film of about 650 nanometers stacked on one another. The NSG film can suppress variation in resistance. The PSG film can increase strength of wire bonding.

A pair of first electrodes (front surface electrodes) 5 a and 5 b and a relay wire 5 c are provided on the second insulating film 4. The first electrode 5 a of the paired first electrodes 5 a and 5 b is allocated above the first insulating film 2 a, and one end of the first electrode 5 a horizontally overlaps with one end of the resistive layer 3 a in the depth direction. The other first electrode 5 b is allocated above the first insulating film 2 b, and one end of the first electrode 5 b horizontally overlaps with one end of the resistive layer 3 b in the depth direction. The relay wire 5 c is interposed between the pair of the first electrodes 5 a and 5 b and spans over the first insulating film 2 a and the first insulating film 2 b.

The first electrode 5 a of the paired first electrodes 5 a and 5 b is connected to one end of the resistive layer 3 a via a contact region 6 a. The other end of the resistive layer 3 a is connected to a resistive-layer connection terminal at one end (a first end) of the relay wire 5 c via a contact region 6 b. The other first electrode 5 b is connected to one end of the resistive layer 3 b via a contact region 6 c. The other end of the resistive layer 3 b is connected to a resistive-layer connection terminal at another end (a second end) of the relay wire 5 c via a contact region 6 d. A substrate connection terminal at still another end (a third end) of the relay wire 5 c is connected to the semiconductor substrate 1 with an ohmic contact at low contact resistance via a contact region 6 e. A second electrode 9 is deposited on the rear side of the semiconductor substrate 1. The resistive layers 3 a and 3 b are thus connected to the semiconductor substrate 1 in series via the relay wire 5 c, so as to exhibit a vertical-type resistive element to provide a resistor between the first electrode 5 a and the second electrode 9.

A thickness of the pair of the first electrodes 5 a and 5 b and the relay wire 5 c is about three micrometers, for example. The pair of the first electrodes 5 a and 5 b and the relay wire 5 c may be a stacked film including a titanium-titanium nitride (Ti—TiN) film of about 120 nanometers serving as barrier metal, an aluminum-silicon (Al—Si) film of about three micrometers, and a TiN—Ti film of about 45 nanometers serving as a reflection preventing film. Instead of Al—Si, Al or an Al alloy such as Al—Cu—Si and Al—Cu may be used. The pair of the first electrodes 5 a and 5 b each serve as an electrode pad. A bonding wire (not shown) having a diameter of about 300 micrometers made of metal such as Al is connected to the respective first electrodes 5 a and 5 b.

A guard ring layer 5 d is deposited on the second insulating film 4. The guard ring layer 5 d is delineated into a ring shape at an outer periphery of a chip of the resistive element according to the embodiment of the present invention. The guard ring layer 5 d is connected to the semiconductor substrate 1 via contact regions 6 f and 6 g. The guard ring layer 5 d is made of the same material as the pair of the first electrodes 5 a and 5 b and the relay wire 5 c. The guard ring layer 5 d prevents moisture from entering from the side surface of the chip.

A passivation film 7 is deposited on the pair of the first electrodes 5 a and 5 b, the relay wire 5 c, and the guard ring layer 5 d. The passivation film 7 may be a composite film including a TEOS film, a Si₃N₄ film, and a polyimide film sequentially stacked. The passivation film 7 is provided with openings 7 a and 7 b. The first electrodes 5 a and 5 b are exposed to the openings 7 a and 7 b to serve as pad regions connected with the bonding wire.

FIG. 3 is a plan view of the resistive element according to the embodiment of the present invention. FIG. 1 is the cross-sectional view as viewed from direction A-A in FIG. 3. The resistive element according to the embodiment of the present invention has a rectangular planar pattern with a longitudinal direction in which the pair of the first electrodes 5 a and 5 b and the relay wire 5 c are arranged. The chip of the resistive element according to the embodiment of the present invention has a size of about 2.8 millimeters×2.5 millimeters, for example. As illustrated in FIG. 3, the first electrode 5 a of the paired first electrodes 5 a and 5 b allocated on the left side has a rectangular planar pattern having a length L₁ and a width W₁, which is the same as that of the other first electrode 5 b allocated on the right side. The first electrode 5 a and the other first electrode 5 b are arranged in parallel and separated with a space S₁. The length L₁ is about 2.0 millimeters, a width W₁ is about 0.9 millimeters, and the space Si is about 0.5 millimeters or greater, for example. As illustrated in FIG. 3, the resistive layers 3 a and 3 b and the relay wire 5 c also have a rectangular planar pattern with a longitudinal direction which is the vertical direction in FIG. 3.

The relay wire 5 c having a rectangular planar pattern is allocated on the straight line L2 passing through the center C1 of the chip. The resistive layers 3 a and 3 b, the pair of the first electrodes 5 a and 5 b, and the relay wire 5 c are arranged with line symmetry about the straight line L2 passing through the center C1 of the chip in the planar pattern. The planar pattern of the resistive layers 3 a and 3 b, the pair of the first electrodes 5 a and 5 b, and the relay wire 5 c has two-fold rotational symmetry about the center C1 of the chip. The arrangement of the two-fold rotational symmetry enables the use of the resistive element turned by 180 degrees and thus facilitates an assembling process of the resistive element.

As illustrated in FIG. 1, the second electrode (rear surface electrode) 9 is deposited on the bottom surface of the semiconductor substrate 1. The second electrode 9 may be a single film made of gold (Au) or a metallic film including a Ti film, a Ni film and a Au film stacked in this order. The outermost layer of the second electrode 9 may be made of a material which can be soldered. The second electrode 9 is fixed to a metallic plate (not shown) by soldering.

FIG. 4 is a cross-sectional view in which an equivalent circuit is superposed on the cross-sectional structure on the left side of the resistive element according to the embodiment of the present invention illustrated in FIG. 1. A terminal 101 is connected to the first electrode 5 a of the paired first electrodes 5 a and 5 b, and a terminal 102 is connected to the second electrode 9. A parasitic capacitance C_(pad) is provided below the first electrode 5 a to use the first insulating film 2 a and the second insulating film 4 as a dielectric material. A parasitic capacitance C_(poly) is provided below the resistive layer 3 a to use the first insulating film 2 a as a dielectric material. A parasitic capacitance C_(pmm) allocated between one end of the first electrode 5 a and one end (the resistive-layer connection terminal) of the relay wire 5 c where the passivation film 7 is used as a dielectric material, is small and thus can be ignored.

FIG. 5A is a circuit diagram of the equivalent circuit illustrated in FIG. 4. The parasitic capacitance C_(poly) allocated below the resistive layer 3 a and using the first insulating film 2 a as a dielectric material is presumed to be connected in parallel to a resistor R_(poly) of the resistive layer 3 a. The parasitic capacitance C_(pad) and the parasitic capacitance C_(poly) are combined to provide a parasitic capacitance C_(para), as illustrated in FIG. 5B. If an impedance of the parasitic capacitance C_(para) is lower than the chip resistor R_(poly), a current I_(C) flowing through the parasitic capacitance C_(para) would be dominant, leading to oscillation. In order to prevent such oscillation, the parasitic capacitance C_(para) should be calculated and confirmed with respect to a required cutoff frequency. The condition for preventing oscillation is that a current I_(PAD) flowing through the chip is substantially equal to a current component I_(R) flowing through the chip resistor R_(poly). A low-pass filter is represented by the following equation (1): f _(c)=1/(2πC _(para) R _(poly))  (1) where f_(c) is an oscillation frequency. The equation (1) can be changed to the following equation (2): C _(para)=1/(2πf _(c) R _(poly))  (2)

The oscillation frequency f_(c) is substituted into the equation (2) so as to calculate the parasitic capacitance C_(para). Setting the parasitic capacitance C_(para) to the calculated value or lower can ensure the current component I_(R) flowing through the chip resistor R_(poly) so as to prevent oscillation. The parasitic capacitance C_(para) can be controlled by adjusting the thicknesses of the first insulating film 2 a and the second insulating film 4.

A contact arrangement at the contact regions 6 a and 6 b connecting the resistive layer 3 a to the first electrode 5 a and the relay wire 5 c illustrated in FIG. 1, is described below with reference to FIG. 6 to FIG. 8. While the following explanations with reference to FIG. 6 to FIG. 8 are focused on the resistive layer 3 a, a similar contact arrangement can be used for the contact regions 6 c and 6 d connecting the resistive layer 3 b to the other first electrode 5 b and the relay wire 5 c.

In the following explanations with reference to FIG. 6 to FIG. 8, a direction in which the length L₁ of the first electrode 5 a illustrated in the planar pattern of FIG. 3 is measured is defined as a resistance width direction, and a direction in which the width W₁ of the first electrode 5 a is measured is defined as a resistance length direction. The resistance length direction is a main direction of the current components flowing through the resistive layer 3 a, as indicated by the broken line arrows in FIG. 7. The space S₁ illustrated in FIG. 3 is also measured in the resistance length direction. The term “resistance length direction” as used herein refers to a main direction of flow of current in which the resistivity of the resistive layer 3 a is determined on a macro level. Although the current components indicated by the broken line arrows in FIG. 6 vary in angle, the current components mainly flow in the resistance length direction when divided into vector components.

As illustrated in FIG. 6, first outer contacts 61 a to 61 d and first inner contacts 62 a to 62 d closer to the middle (the inner side) of the resistive layer 3 a than the first outer contacts 61 a to 61 d, are allocated toward one end (a first end) 31 of the resistive layer 3 a. The first inner contacts 62 a to 62 d are aligned periodically in the resistance width direction. The first outer contacts 61 a to 61 d are arranged parallel to the first inner contacts 62 a to 62 d and aligned periodically in the resistance width direction. The first inner contacts 62 a to 62 d and the first outer contacts 61 a to 61 d are shifted from each other in a zigzag (checkered) pattern in the resistance width direction so as not to overlap each other.

Second outer contacts 64 a to 64 d and second inner contacts 63 a to 63 d closer to the middle (the inner side) of the resistive layer 3 a than the outer contacts 64 a to 64 d, are allocated toward the other end (a second end) 32 of the resistive layer 3 a opposite to the first end 31 in the resistance length direction. The second inner contacts 63 a to 63 d are aligned periodically in the resistance width direction. The second outer contacts 64 a to 64 d are arranged parallel to the second inner contacts 63 a to 63 d and aligned periodically in the resistance width direction. The second inner contacts 63 a to 63 d and the second outer contacts 64 a to 64 d are shifted from each other in a zigzag (checkered) pattern in the resistance width direction so as not to overlap each other.

The first inner contacts 62 a to 62 d and the second inner contacts 63 a to 63 d are shifted from each other in the resistance width direction so as not to overlap each other. The first inner contacts 62 a to 62 d are opposed to the second outer contacts 64 a to 64 d through the respective gaps between the second inner contacts 63 a to 63 d, as viewed in the resistance length direction. The second inner contacts 63 a to 63 d are opposed to the first outer contacts 61 a to 61 d through the respective gaps between the first inner contacts 62 a to 62 d, as viewed in the resistance length direction.

While FIG. 6 illustrates that the width of the respective gaps between the second inner contacts 63 a to 63 d is identical to the length of the second outer contacts 64 a to 64 d in the resistance width direction, the width and the length may be different from each other. For example, the respective gaps between the second inner contacts 63 a to 63 d illustrated in FIG. 6 may be decreased so that the first inner contacts 62 a to 62 d are partly opposed to the second outer contacts 64 a to 64 d. Alternatively, the respective gaps between the second inner contacts 63 a to 63 d illustrated in FIG. 6 may be increased so as to provide spaces where the second inner contacts 63 a to 63 d and the second outer contacts 64 a to 64 d are not present as viewed in the resistance length direction.

Similarly, the width of the respective gaps between the first inner contacts 62 a to 62 d is identical to the length of the first outer contacts 61 a to 61 d in the resistance width direction, but the width and the length may be different from each other. For example, the respective gaps between the first inner contacts 62 a to 62 d illustrated in FIG. 6 may be decreased so that the second inner contacts 63 a to 63 d are partly opposed to the first outer contacts 61 a to 61 d. Alternatively, the respective gaps between the first inner contacts 62 a to 62 d illustrated in FIG. 6 may be increased so as to provide spaces where the first inner contacts 62 a to 62 d and the first outer contacts 61 a to 61 d are not present as viewed in the resistance length direction.

A distance D1 between the first inner contacts 62 a to 62 d and the second outer contacts 64 a to 64 d is preferably, but not necessarily, identical to a distance D2 between the second inner contacts 63 a to 63 d and the first outer contacts 61 a to 61 d. For example, the distance D1 may be greater than the distance D2, or the distance D1 may be smaller than the distance D2. The distance D1 between the respective pairs of the first inner contacts 62 a to 62 d and the second outer contacts 64 a to 64 d opposed to each other may be either the same or different from each other. The distance D2 between the respective pairs of the second inner contacts 63 a to 63 d and the first outer contacts 61 a to 61 d opposed to each other may be either the same or different from each other.

FIG. 7 illustrates a contact arrangement of a comparative example. In the contact arrangement of the comparative example, the positions of the first inner contacts 62 a to 62 d and the first outer contacts 61 a to 61 d in the resistance width direction on the first end 31 side overlap each other as viewed in the resistance length direction. Similarly, the positions of the second inner contacts 63 a to 63 d and the second outer contacts 64 a to 64 d in the resistance width direction on the second end 32 side overlap each other as viewed in the resistance length direction. The positions of the first inner contacts 62 a to 62 d and the second inner contacts 63 a to 63 d in the resistance width direction also overlap each other as viewed in the resistance length direction.

In the contact arrangement illustrated in FIG. 7, the first inner contacts 62 a to 62 d aligned in the resistance width direction and the second inner contacts 63 a to 63 d aligned in the resistance width direction are opposed to each other as viewed in the resistance length direction. The second outer contacts 64 a to 64 d aligned in the resistance width direction are thus hidden behind the second inner contacts 63 a to 63 d as viewed in the resistance length direction. The first outer contacts 61 a to 61 d aligned in the resistance width direction are also hidden behind the first inner contacts 62 a to 62 d as viewed in the resistance length direction. As indicated by the broken line arrows in FIG. 7, current components flowing through the resistive layer 3 a are uneven, and current tends to be concentrated around the first inner contacts 62 a to 62 d and the second inner contacts 63 a to 63 d opposed to each other with the shortest distance in the resistance length direction.

In contrast, the contact arrangement illustrated in FIG. 6 having larger effective contact areas allows the current components to be uniform in the contacts, as indicated by the broken line arrows in FIG. 6, so as to prevent current concentration from varying depending on the contacts. The prevention of current concentration enhances the resistance to surge current with less variation in the resistivity.

Alternatively, as illustrated in FIG. 8, the resistive element may have a contact arrangement with a first outer contact 61 and a second outer contact 64 each having a linear (line) pattern extending in the resistance width direction. The arrangements of the first inner contacts 62 a to 62 d and the second inner contacts 63 a to 63 d are the same as in the contact arrangement illustrated in FIG. 6. The first inner contacts 62 a to 62 d aligned in the resistance width direction are partly opposed to the second outer contact 64 through the respective gaps between the second inner contacts 63 a to 63 d, as viewed in the resistance length direction. The second inner contacts 63 a to 63 d aligned in the resistance width direction are partly opposed to the first outer contact 61 through the respective gaps between the first inner contacts 62 a to 62 d, as viewed in the resistance length direction.

The contact arrangement illustrated in FIG. 8 having larger effective contact areas allows the current components to be uniform in the contacts, so as to prevent current concentration from varying depending on the contacts, as in the case of the contact arrangement illustrated in FIG. 6. The prevention of current concentration enhances the resistance to surge current with less variation in the resistivity.

The resistive element according to the embodiment of the present invention can be used for an inverter module 100 for driving a three-phase motor having a u-phase, a v-phase, and a w-phase, for example, as illustrated in FIG. 9. The inverter module 100 includes power semiconductor devices TR1, TR2, TR3, and TR4 for driving the u-phase, power semiconductor devices TR5, TR6, TR7, and TR8 for driving the v-phase, and power semiconductor devices TR9, TR10, TR11, and TR12 for driving the w-phase. The power semiconductor devices TR1 to TR12 are each connected to a freewheeling diode (not shown). The power semiconductor devices TR1 to TR12 may be IGBTs, and gate electrodes of the IGBTs are connected to gate resistors R1 to R12 in order to suppress an oscillation phenomenon upon switching operation.

The resistive element according to the embodiment of the present invention can be used as each of a pair of the gate resistors R1 and R2, a pair of the gate resistors R3 and R4, a pair of the gate resistors R5 and R6, a pair of the gate resistors R7 and R8, a pair of the gate resistors R9 and R10, and a pair of the gate resistors R11 and R12. For example, the resistive layers 3 a and 3 b illustrated in FIG. 1 correspond to the gate resistors R1 and R2. The side on which the gate resistors R1 and R2 are connected to the gate electrodes of the power semiconductor devices TR1 and TR2 corresponds to each terminal of the pair of the first electrodes 5 a and 5 b illustrated in FIG. 1. The side opposite to the side on which the gate resistors R1 and R2 are connected to the gate electrodes of the power semiconductor devices TR1 and TR2 corresponds to the terminal of the second electrode 9 illustrated in FIG. 1.

The resistive element according to the embodiment of the present invention includes the first inner contacts 62 a to 62 d and the second inner contacts 63 a to 63 d which are shifted from each other as viewed in the resistance length direction of the contact arrangement connecting the resistive layer 3 a to the first electrode 5 a and the relay wire 5 c, as illustrated in FIG. 6. The first inner contacts 62 a to 62 d are opposed to the second outer contacts 64 a to 64 d in the resistance length direction. The second inner contacts 63 a to 63 d are opposed to the first outer contacts 61 a to 61 d in the resistance length direction. The distance D1 between the first inner contacts 62 a to 62 d and the second outer contacts 64 a to 64 d is substantially the same as the distance D2 between the second inner contacts 63 a to 63 d and the first outer contacts 61 a to 61 d. Accordingly, the effective contact areas can be increased, so as to avoid unevenness of the current components in the respective contacts.

In the resistive element according to the embodiment of the present invention, the resistive-layer connection terminals at two ends of the relay wire 5 c are connected to the resistive layers 3 a and 3 b, and the substrate connection terminal at another end of the relay wire 5 c is connected to the semiconductor substrate 1 having a low specific resistivity with an ohmic contact at low contact resistance, so as to exhibit a vertical-type resistive element. Each of the resistive layers 3 a and 3 b is connected to a single pad region which is a part of each of the pair of the first electrodes 5 a and 5 b on the top surface side. The vertical-type resistive element thus requires only a single bonding wire for each of the resistive layers 3 a and 3 b, so as to decrease the total number of bonding wires, as compared with a lateral-type resistive element. Further, the areas of the pad regions on the top surface side of the first electrodes 5 a and 5 b can be decreased in the vertical-type resistive element, as compared with a lateral-type resistive element, and the size of the chip can be reduced accordingly.

A method of manufacturing the resistive element according to the embodiment of the present invention is illustrated below with reference to FIG. 10 to FIG. 19. It should be understood that the method of manufacturing the resistive element described below is a mere example, and the embodiment of the present invention can implement various methods other than the following method including modified examples within the scope of the invention as defined by the following appended claims.

First, the semiconductor substrate 1, such as a silicon substrate, doped with a high concentration of n-type impurity ions is prepared. As illustrated in FIG. 10, a first insulating film 2 such as a TEOS film is deposited on the semiconductor substrate 1 by a low-pressure (LP) CVD method, for example. The first insulating film 2 may be a composite film obtained such that a thermal oxide film is formed by a thermal oxidation method, and an insulating film is then stacked on the thermal oxide film by a CVD method. A photoresist film is then coated on the top surface of the first insulating film 2, and is delineated by photolithography. Using the delineated photoresist film as an etching mask, a part of the first insulating film 2 is selectively removed by dry etching such as reactive ion etching (RIE). The photoresist film is then removed, so as to form the first insulating films 2 a and 2 b partly on the top surface of the semiconductor substrate 1, as illustrated in FIG. 11.

Next, a non-doped polysilicon layer is formed on the semiconductor substrate 1 and the first insulating films 2 a and 2 b by a CVD method. N-type impurity ions such as phosphorus (P) are implanted in the polysilicon layer. For example, P impurity ions are implanted under the conditions of an acceleration voltage of 80 keV and a dose of about 6.0×10¹⁵ cm⁻² or less. The impurity ions implanted by annealing are activated, so as to form a doped polysilicon layer 3 doped with the highly-concentrated n-type impurity ions, as illustrated in FIG. 12. A photoresist film is then coated on the top surface of the doped polysilicon film 3, and is delineated by photolithography. Using the delineated photoresist film as an etching mask, a part of the doped polysilicon layer 3 is selectively removed by RIE. The photoresist film is then removed, so as to form the resistive layers 3 a and 3 b on the first insulating films 2 a and 2 b, respectively, as illustrated in FIG. 13.

Next, as illustrated in FIG. 14, the second insulating film 4 is deposited to cover the first insulating films 2 a and 2 b and the resistive layers 3 a and 3 b. The second insulating film 4 may be made of a composite film including a NSG film and a PSG film sequentially stacked by a CVD method, for example. A photoresist film is then coated on the second insulating film 4, and is delineated by photolithography. Using the delineated photoresist film as an etching mask, a part of the second insulating film 4 is selectively removed by RIE. The photoresist film is then removed, so as to open a first contact hole 4 a and a second contact hole 4 b on one side, a first contact hole 4 c and a second contact hole 4 d on the other side, and a third contact hole 4 e in the second insulating film 4, as illustrated in FIG. 15. The second insulating film 4 is also provided with a fourth contact hole 4 f on one side and a fourth contact hole 4 g on the other side simultaneously.

Next, as illustrated in FIG. 16, a metallic film 5 is deposited on the second insulating film 4 to fill the contact holes 4 a to 4 g by vacuum evaporation or sputtering. The metallic film 5 may be made of a Ti—TiN film, an Al—Si film, and a TiN—Ti film sequentially stacked by a CVD method, for example. A photoresist film is then coated on the metallic film 5, and is delineated by photolithography. Using the delineated photoresist film as an etching mask, a part of the metallic film 5 is selectively removed, so as to form the pair of the first electrodes 5 a and 5 b, the relay wire 5 c, and the guard ring layer 5 d on the second insulating film 4, as illustrated in FIG. 17.

At the same time, the respective contact regions 6 a to 6 g are formed. The contact region 6 a connects the first electrode 5 a of the paired first electrodes 5 a and 5 b to the resistive layer 3 a via the first contact hole 4 a on one side, and the contact region 6 b connects the first electrode 5 a to the relay wire 5 c via the second contact hole 4 b on one side. The contact region 6 e connects the relay wire 5 c to the semiconductor substrate 1 via the third contact hole 4 e. The contact region 6 c connects the other first electrode 5 b to the resistive layer 3 b via the first contact hole 4 c on the other side, and the contact region 6 d connects the other first electrode 5 b to the relay wire 5 c via the second contact hole 4 d on the other side. The contact regions 6 f and 6 g connect the guard ring layer 5 d to the semiconductor substrate 1 via the fourth contact hole 4 f on one side and the fourth contact hole 4 g on the other side.

Next, as illustrated in FIG. 18, the passivation film 7 is formed on the pair of the first electrodes 5 a and 5 b, the relay wire 5 c, and the guard ring layer 5 d. The passivation film 7 is formed such that a TEOS film and a Si₃N₄ film are sequentially stacked, and a polyimide film is further coated on the stacked film by a plasma CVD method, for example. A photoresist film is then coated on the passivation film 7, and is delineated by photolithography. Using the delineated photoresist film as an etching mask, a part of the passivation film 7 is selectively removed, so as to open the openings 7 a and 7 b in the passivation film 7 as illustrated in FIG. 19. The first electrodes 5 a and 5 b are exposed to the openings 7 a and 7 b to serve as pad regions.

Next, the bottom surface of the semiconductor substrate 1 is polished by chemical mechanical polishing (CMP) so as to decrease the thickness of the semiconductor substrate 1 to about 350 micrometers. The second electrode 9 is then formed on the bottom surface of the semiconductor substrate 1 by vacuum evaporation or sputtering. A plurality of elements, each substantially corresponding to the resistive element illustrated in FIG. 1, are formed in chip regions arranged into a matrix form in a single wafer. The chip regions are diced and divided into chips each corresponding to the resistive element illustrated in FIG. 1.

The method of manufacturing the resistive element according to the embodiment of the present invention facilitates the fabrication of the resistive element with the chip size reduced and the number of bonding wires decreased.

First Modified Example

A resistive element according to a first modified example of the embodiment of the present invention illustrated in FIG. 20 differs from the resistive element illustrated in FIG. 1 in further including auxiliary films 3 c and 3 d in a floating state in terms of potential allocated on the first insulating films 2 a and 2 b and separated from the resistive layers 3 a and 3 b.

The auxiliary film 3 c is deposited below the first electrode 5 a of the paired first electrodes 5 a and 5 b and separated from the resistive layer 3 a. The auxiliary film 3 d is deposited below the other first electrode 5 b and separated from the resistive layer 3 b. The auxiliary films 3 c and 3 d are made of the same material as the resistive layers 3 a and 3 b, such as n-type doped polysilicon, and have the same thickness as the resistive layers 3 a and 3 b. The auxiliary films 3 c and 3 d have a rectangular planar pattern, for example. The other structures in the resistive element according to the first modified example of the embodiment of the present invention are the same as those in the resistive element illustrated in FIG. 1 described above, and overlapping explanations are not repeated below.

The resistive element according to the first modified example of the embodiment of the present invention includes the auxiliary films 3 c and 3 d in a floating state in terms of potential allocated on the first insulating films 2 a and 2 b, so as to reduce the parasitic capacitance below the pair of the first electrodes 5 a and 5 b, as in the case of increasing the thickness of the first insulating films 2 a and 2 b. The resistive element according to the first modified example thus can avoid a decrease in the total resistance with respect to a reduction in impedance during operation at a high frequency so as to prevent oscillation.

A method of manufacturing the resistive element according to the first modified example of the embodiment of the present invention may form the auxiliary films 3 c and 3 d simultaneously with the resistive layers 3 a and 3 b by selectively removing the doped polysilicon layer 3 in the step illustrated in FIG. 13. The other steps of the method of manufacturing the resistive element according to the first modified example are the same as those of the method according to the embodiment described above, and overlapping explanations are not repeated below.

Second Modified Example

The resistive element according to the embodiment of the present invention described above includes the plural first insulating films 2 a and 2 b, resistive layers 3 a and 3 b, and first electrodes 5 a and 5 b, and the single relay wire 5 c electrically connected to each one end of the resistive layers 3 a and 3 b, as illustrated in FIG. 1. A resistive element according to a second modified example of the embodiment of the present invention illustrated in FIG. 21 differs from the resistive element illustrated FIG. 1 in including a plurality of resistive layers 3 a and 3 b and relay wires 5 f and 5 g, and a single first electrode 5 e electrically connected to each one end of the resistive layers 3 a and 3 b.

An auxiliary film 3 e in a floating state in terms of potential is deposited on a first insulating film 2 c and separated from the resistive layers 3 a and 3 b so as to be interposed between the resistive layers 3 a and 3 b. The auxiliary layer 3 e is made of the same material as the resistive layers 3 a and 3 b, such as n-type doped polysilicon, and has the same thickness as the resistive layers 3 a and 3 b. The auxiliary layer 3 e has a rectangular planar pattern, for example. The single first electrode 5 e is deposited on the second insulating film 4 and allocated in the middle of the chip. The paired relay wires 5 f and 5 g are deposited on the second insulating film 4 to interpose the first electrode 5 e. One end of the first electrode 5 e overlaps with one end of the resistive layer 3 a in the depth direction, and the other end of the first electrode 5 e overlaps with one end of the resistive layer 3 b in the depth direction. One end of the relay wire 5 f of the paired relay wires 5 f and 5 g overlaps with the other end of the resistive layer 3 a in the depth direction. One end of the other relay wire 5 g overlaps with the other end of the resistive layer 3 b in the depth direction.

The first electrode 5 e is connected to one end of the resistive layer 3 a via a contact region 6 b. The other end of the resistive layer 3 a is connected to a resistive-layer connection terminal at one end of the relay wire 5 f of the paired relay wires 5 f and 5 g via a contact region 6 a. A substrate connection terminal at the other end of the relay wire 5 f is connected to the semiconductor substrate 1 with an ohmic contact via a contact region 6 h. The first electrode 5 e is also connected to one end of the resistive layer 3 b via a contact region 6 d. The other end of the resistive layer 3 b is connected to a resistive-layer connection terminal at one end of the other relay wire 5 g via a contact region 6 c. A substrate connection terminal at the other end of the other relay wire 5 g is connected to the semiconductor substrate 1 with an ohmic contact via a contact region 6 i.

The resistive layers 3 a and 3 b are thus connected to the semiconductor substrate 1 in series via the pair of the relay wires 5 f and 5 g, so as to exhibit a vertical-type resistive element to provide a resistor between the first electrode 5 e and the second electrode 9. The other structures in the resistive element according to the second modified example of the embodiment of the present invention are the same as those in the resistive element illustrated in FIG. 1 described above, and overlapping explanations are not repeated below.

The resistive element according to the second modified example of the embodiment of the present invention includes the pair of the relay wires 5 f and 5 g connecting the resistive layers 3 a and 3 b to the semiconductor substrate 1 in series to provide a resistor between the first electrode 5 e and the second electrode 9. The resistive layers 3 a and 3 b are connected to a single pad region which is a part of the first electrode 5 e on the top surface side. The resistive element according to the second modified example thus requires only a single bonding wire, so as to decrease the total number of bonding wires, as compared with a lateral-type resistive element. Further, the area of the pad region on the top surface side of the first electrode 5 e can be decreased as compared with a lateral-type resistive element, and the size of the chip can be reduced accordingly.

The arrangement of the auxiliary film 3 e in a floating state in terms of potential deposited on the first insulating film 2 c can reduce the parasitic capacitance, as in the case of increasing the thickness of the first insulating film 2 c. The resistive element according to the second modified example thus can avoid a decrease in the total resistance with respect to a reduction in impedance during operation at a high frequency so as to prevent oscillation.

A method of manufacturing the resistive element according to the second modified example of the embodiment of the present invention may form the auxiliary film 3 e simultaneously with the resistive layers 3 a and 3 b by selectively removing the doped polysilicon layer 3 in the step illustrated in FIG. 13. The resistive element according to the second modified example differs from the resistive element according to the embodiment illustrated in FIG. 1 in the arrangement positions and the number of the first insulating film 2 c, the resistive layers 3 a and 3 b, the first electrode 5 e, and the pair of the relay wires 5 f and 5 g, for example. However, the other steps of the method of manufacturing the resistive element according to the second modified example are the same as those of the method according to the embodiment described above, and overlapping explanations are not repeated below.

Other Embodiments

While the present invention has been described above by reference to the embodiment, it should be understood that the present invention is not intended to be limited to the descriptions of the Specification and the drawings composing part of this disclosure. Various alternative embodiments, examples, and technical applications will be apparent to those skilled in the art according to this disclosure.

While the embodiment of the present invention has illustrated the resistive element including the two resistive layers 3 a and 3 b in one chip as illustrated in FIG. 1, each chip may be provided with a single resistive layer. The resistive element illustrated in FIG. 1 may eliminate the structure on the right side including the first insulating film 2 b, the resistive layer 3 b, and the first electrode 5 b. The resistive element illustrated in FIG. 20 may eliminate the structure on the right side including the first insulating film 2 b, the resistive layer 3 b, the first electrode 5 b, and the auxiliary film 3 d. The resistive element illustrated in FIG. 21 may eliminate the structure on the right side including the resistive layer 3 b and the relay wire 5 g. Alternatively, three or more resistive layers may be provided in a single chip.

The embodiment of the present invention has exemplified the case in which the resistive element is used as the gate resistors R1 to R12, as illustrated in FIG. 9. However, the resistive element is not limited to be used as the gate resistors R1 to R12, and may be used as a resistive element for various types of integrated circuit (IC). The contact arrangement of the resistive element according to the embodiment of the present invention may be applied to the fabrication of a resistive element for various types of IC. For example, the contact arrangement according to the embodiment of the present invention may be used for a lateral-type resistive element including two electrodes on a top surface of a resistive layer.

The embodiment of the present invention has illustrated the resistive element having the two rows of the first outer contacts 61 a to 61 d and the first inner contacts 62 a to 62 d at one end of the resistive layer 3 a and the two rows of the second inner contacts 63 a to 63 d and the second outer contacts 64 a to 64 d at the other end of the resistive layer 3 a. Alternatively, the resistive element may have three or more rows of contacts in the resistance length direction at both ends of the resistive layer 3 a, each row including the contacts aligned in the resistance width direction. When there are three rows of contacts at both ends of the resistive layer 3 a, each set of the first inner contacts 62 a to 62 d and the second inner contacts 63 a to 63 d aligned in the resistance width direction may be arranged in the front row closest to the middle of the resistive layer 3 a. Each set of the first outer contacts 61 a to 61 d and the second outer contacts 64 a to 64 d aligned in the resistance width direction may be arranged in the second row away from the middle of the resistive layer 3 a. 

What is claimed is:
 1. A resistive element comprising: a resistive layer having a rectangular shape defined by a resistance length direction and a resistance width direction orthogonal to the resistance length direction; a first outer contact allocated on one side of the resistive layer defined in the resistive length direction; a first inner contact allocated on the one side of the resistive layer closer to a middle of the resistive layer than the first outer contact in the resistance length direction; a second outer contact allocated on another side of the resistive layer defined in the resistive length direction; and a second inner contact allocated on the other side of the resistive layer closer to the middle of the resistive layer than the second outer contact in the resistance length direction, wherein, as viewed in the resistance length direction, the first inner contact is shifted from the second inner contact, the first inner contact is at least partly opposed to the second outer contact, and the second inner contact is at least partly opposed to the first outer contact.
 2. The resistive element of claim 1, wherein a distance between the first inner contact and the second outer contact opposed to each other is identical to a distance between the second inner contact and the first outer contact opposed to each other.
 3. The resistive element of claim 1, wherein: the resistive element comprises a set of the first inner contacts, a set of the second inner contacts, a set of the first outer contacts, and a set of the second outer contacts, the contacts in each set being aligned in the resistance width direction; and as viewed in the resistance length direction, positions of the first inner contacts in the resistance width direction are shifted from positions of the second inner contacts in the resistance width direction, the positions of the first inner contacts in the resistance width direction are opposed to positions of the second outer contacts in the resistance width direction, and the positions of the second inner contacts in the resistance width direction are opposed to positions of the first outer contacts in the resistance width direction.
 4. The resistive element of claim 1, wherein: the resistive element comprises a set of the first inner contacts and a set of the second inner contacts, the contacts in each set being aligned in the resistance width direction; and as viewed in the resistance length direction, positions of the first inner contacts in the resistance width direction are shifted from positions of the second inner contacts in the resistance width direction, the positions of the first inner contacts in the resistance width direction are partly opposed to a position of the second outer contact extending in a line pattern in the resistance width direction, and the positions of the second inner contacts in the resistance width direction are partly opposed to a position of the first outer contact extending in a line pattern in the resistance width direction. 